Port FDS to more accurate emulation

[nyanpasu64]

todo:

• [x] squash "Rename CFDS::m_Fds to m_FDS" into my earlier commits
• [x] get rid of std::optional to improve performance
• [x] check to see the two blip_buffers are creating latency or not
  • 9 samples of latency, this is bad
  • fixed: 8 samples of latency from mix_samples()
  • fixed: 1 sample of latency from read_samples()
• [x] implement "cycles until level change"
  • [x] switch to mesen, the emulation there is more deterministic
  • [x] check if mesen is accurate
    • dreadful quantization due to uint8 output, likely not hardware accurate
    • fixed
• [x] fix volume meters
• [x] fix volume mixing levels
  • when testing famitracker with nsfplay 2a03 and mesen fds ("volume comparison pulse fds.0cc"), the 2a03 vs. fds volume balance is closest when the meter is set to +1dB.
  • 10^(1/20) = 1.12201845430196343559
• [x] licensing: mesen is gplv3, fami is gplv2+
• [x] remove wall of text from CMixer

[nyanpasu64]

Fixed by #32.